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Sharing the slope: depth partitioning of agariciid corals and associated Symbiodinium across shallow and mesophotic habitats
(2-60 m) on a Caribbean reef.

Journal

BMC Evolutionary Biology

Volume

13

Pages (from-to)

205

Number of pages

15

Document type

Article

Faculty

Faculty of Science (FNWI)

Institute

Institute for Biodiversity and Ecosystem Dynamics (IBED)

Abstract

Background

Scleractinian corals and their algal endosymbionts (genus Symbiodinium) exhibit distinct bathymetric distributions
on coral reefs. Yet, few studies have assessed the evolutionary context of these ecological distributions by exploring the
genetic diversity of closely related coral species and their associated Symbiodinium over large depth ranges. Here we assess
the distribution and genetic diversity of five agariciid coral species (Agaricia humilis, A. agaricites, A. lamarcki, A. grahamae,
and Helioseris cucullata) and their algal endosymbionts (Symbiodinium) across a large depth gradient (2-60 m) covering shallow
to mesophotic depths on a Caribbean reef.Results

The five agariciid species exhibited distinct depth distributions,
and dominant Symbiodinium associations were found to be species-specific, with each of the agariciid species harbouring a
distinct ITS2-DGGE profile (except for a shared profile between A. lamarcki and A. grahamae). Only A. lamarcki harboured different
Symbiodinium types across its depth distribution (i.e. exhibited symbiont zonation). Phylogenetic analysis (atp6) of the coral
hosts demonstrated a division of the Agaricia genus into two major lineages that correspond to their bathymetric distribution
("shallow": A. humilis / A. agaricites and "deep": A. lamarcki / A. grahamae), highlighting the role of depth-related factors
in the diversification of these congeneric agariciid species. The divergence between "shallow" and "deep" host species was
reflected in the relatedness of the associated Symbiodinium (with A. lamarcki and A. grahamae sharing an identical Symbiodinium
profile, and A. humilis and A. agaricites harbouring a related ITS2 sequence in their Symbiodinium profiles), corroborating
the notion that brooding corals and their Symbiodinium are engaged in coevolutionary processes.Conclusions

Our
findings support the hypothesis that the depth-related environmental gradient on reefs has played an important role in the
diversification of the genus Agaricia and their associated Symbiodinium, resulting in a genetic segregation between coral
host-symbiont communities at shallow and mesophotic depths.

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